Seal Strength and Package Integrity Testing: A Complete Guide
Representative Infinita Engineering Visual explaining the four-step workflow for Seal Strength Integrity Testing Guide.What Is Seal Strength Testing?
ASTM F88 is the standard method for measuring seal strength in flexible barrier packaging materials — pouches, sachets, and lidding films used in medical, pharmaceutical, and food packaging. It quantifies the force required to peel apart a heat-sealed joint, providing a direct measure of bond quality and integrity, though it does not evaluate package leakage, barrier properties, or shelf life on its own.
Test Configurations
ASTM F88 defines three peel techniques, selected based on packaging construction:
- Technique A (Unsupported): both tails of the specimen are clamped in opposing grips with the seal itself unsupported — common for evaluating “peel-open” seals designed to tear on opening
- Technique B (Supported by Hand, approx. 90 degrees): one tail is manually supported at a 90-degree angle during testing, used where one material tends to curl or deform
- Technique C (Supported by Fixture): the package is held in a support fixture, isolating the seal from stretching in the surrounding flexible material — used for more rigid packaging constructions
Test Procedure
- Cut uniform test strips (commonly 1 inch / 25 mm wide) perpendicular to the seal area
- Select the appropriate technique (A, B, or C) based on packaging construction
- Align the specimen in the grips so the seal line is perpendicular to the pull direction
- Load the specimen on a tensile tester at a constant rate of jaw separation (typically 200-300 mm/min)
- Pull until seal separation occurs, recording the force-vs-displacement curve
- Calculate Maximum Seal Strength (peak force) and Average Seal Strength (mean force over 10-90% of the acquired data points), and document the failure mode
How Critical Is Seal Strength Integrity Testing?
Testing for seal strength compliance is important for the integrity of packages as well as the opening force of flexible materials. Seal testing can gauge a manufacturer’s capacity to provide reliable seals.
The packaging of medical devices frequently uses tests to determine the strength of the seals. Packaging for medical devices must have the ability to maintain sterilization. A sterility breach frequently leads to product returns, expensive replacements, and diminished customer confidence. Medical gadgets may occasionally need a packing system that will keep its integrity when subjected to harsh environmental conditions.
Interpreting Results
Failure mode matters as much as the force value — peeling failure (clean separation at the seal interface) versus material tearing (the substrate fails before the seal does) indicate different underlying issues, and are reported alongside the strength numbers.
Industry Specifications Referencing ASTM F88
- ISO 11607: sterile barrier system validation, requiring seal strength testing as a component
- ASTM F2054: related standard for burst testing of flexible packages
Conclusion
Seal strength testing is as much a process control tool as a material qualification test — consistent seal strength across production batches indicates a stable, well-controlled sealing process, while wide variability often points to a heat-seal parameter (temperature, dwell time, pressure) drifting out of specification.
What is seal strength testing? Seal strength testing measures the force required to separate a package seal. It helps evaluate sealing-process consistency, material compatibility, and the ability of seals to withstand handling and distribution.
What is package integrity testing? Package integrity testing determines whether a package has leaks, channels, holes, or other defects that could compromise product protection. It evaluates the complete package rather than only the mechanical strength of its seals.
What is the difference between seal strength and package integrity? Seal strength measures how strongly two packaging layers are bonded. Package integrity confirms whether the package maintains a continuous barrier against moisture, gases, microorganisms, or product leakage.
What methods are used to detect package leaks? Common methods include bubble emission, dye penetration, vacuum decay, pressure decay, and tracer-gas testing. The appropriate method depends on the package type, expected defect size, and sensitivity required.
What is bubble leak testing? Bubble testing pressurizes a package while it is submerged in liquid. A continuous stream of bubbles indicates a gross leak and may help locate the defect. ASTM F2096 describes this internal-pressurization method.
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